B9.1 Revision notes

9.1 - Chromosomes & Genes
1. Define inheritance
The transmission of genetic information from generation to generation.
2. Define the terms
a. Chromosome as a thread of DNA, made up of a string of genes.
b. Gene as a length of DNA that is the unit of heredity and codes for a specific protein. A gene may be copied
and passed on to the next generation.
c. Allele as any of two or more alternative forms of a gene.
3. Define the terms:
a. Haploid nucleus as a nucleus containing a single set of unpaired chromosomes (e.g. sperm and egg).
b. Diploid nucleus as a nucleus containing two sets of chromosomes (e.g. in body cells).
4. Describe the inheritance of sex in humans (XX and XY chromosomes).
 Of the 23 pairs of chromosomes present in each human cell, one pair is the sex chromosome;
 These determine the sex of the individual;
 Males have XY, and females have XX.